Structural and coordination properties of 3,3-diphenyl-1-(2,4,6-tri-tert- butylphenyl)-2-(trimethylsilyl)-1,3-diphosphapropene derivatives showing interesting conformational features

Article abstract of DOI:10.1021/om050972l

(E)-3,3-Diphenyl-1-(2,4,6-tri-tert-butylphenyl)-2-(trimethylsilyl)-1, 3-diphosphapropene was prepared from (2-(2,4,6-tri-tert-butylphenyl)-1- (trimethylsilyl)-2-phosphaethenyl)lithium and chlorodiphenylphosphine, and the properties involving conformationa

Full text of DOI:10.1021/om050972l

1424
Organometallics 2006, 25, 1424-1430
Structural and Coordination Properties of 3,3-Diphenyl-1-
(2,4,6-tri-tert-butylphenyl)-2-(trimethylsilyl)-1,3-diphosphapropene
Derivatives Showing Interesting Conformational Features
Shigekazu Ito, Katsunori Nishide, and Masaaki Yoshifuji*
Department of Chemistry, Graduate School of Science, Tohoku UniVersity, Aoba, Sendai 980-8578, Japan
ReceiVed NoVember 11, 2005
(E)-3,3-Diphenyl-1-(2,4,6-tri-tert-butylphenyl)-2-(trimethylsilyl)-1,3-diphosphapropene was prepared
from (2-(2,4,6-tri-tert-butylphenyl)-1-(trimethylsilyl)-2-phosphaethenyl)lithium and chlorodiphenylphos-
phine, and the properties involving conformational aspects, coordination to metals, and sulfurization were
investigated. The structure of 2-(trimethylsilyl)-1,3-diphosphapropene shows C1 symmetry with the
phosphino lone pair almost perpendicular to the PdC π-system, whereas the 2-chloro- and 2-methyl-
1,3-diphosphapropene derivatives show nearly Cs symmetry with the phosphino lone pair almost coplanar
with the PdC plane. A very small 2JPP coupling constant for the 2-(trimethylsilyl)-1,3-diphosphapropene
was observed by 31P NMR spectroscopy, indicating that the conformation of the C1 symmetry was kept
in solution. On coordination of the phosphorus atoms to the carbonyltungsten(0) moiety, the inherently
predominant C1 form of the 2-(trimethylsilyl)-1,3-diphosphapropene changed to Cs symmetry. On the
other hand, sulfurization of the 2-(trimethylsilyl)-1,3-diphosphapropene afforded the corresponding
3-thioxo-2-(trimethylsilyl)-1,3-diphosphapropene, indicating C1 symmetry with the PdS bond almost
perpendicular to the PdC moiety. The 2-(trimethylsilyl)-1,3-diphosphapropene acts as a P2 chelate ligand
of a dichloropalladium(II) complex, which showed moderate catalytic activity in the Sonogashira cross-
coupling reaction. The structure of the dichloropalladium(II) complex bearing the ligated 2-(trimethylsilyl)-
1,3-diphosphapropene was analyzed by X-ray crystallography, indicating structure effects on the properties.
Chart 1
Introduction
Phosphaalkenes (methylenephosphines) containing the PdC
moiety have been synthesized since kinetic protection by using
sterically encumbered substituents was established to isolate
various multiply bonded heavier main group elements in the
early 1980s.1,2 As phosphines have been widely utilized as
ligands of metal complexes, phosphaalkenes have attracted much
attention from the point of view of coordination chemistry in
the last two decades. We3 and others1 have reported a consider-
able number of metal complexes bearing ligated phosphaalkenes,
and the coordination properties of the PdC moieties have been
studied. Several phosphaalkenes such as 3,4-diphosphinidenecy-
clobutenes (DPCBs) are available to develop specific catalysts
for organic synthesis.4,5
substituent, we have reported the preparation and coordination
properties of several 1,3-diphosphapropenes 1, which contain
both a low-coordinated sp2-type phosphorus and a normal sp3-
type phosphino phosphorus (Chart 1).6 Such a combination of
an sp3-type phosphorus with an sp2-type phosphorus provides
peculiar ligand design to coordination chemistry. So far, we
have revealed several structural properties of 1,3-diphosphapro-
penes 1 in relation to coordination chemistry as follows. (1)
Basically, the phosphino group of 1 predominantly coordinates
on metals because its basicity is greater than that of the sp2-
type phosphorus.6 (2) As indicated by the molecular structure
of 1, the two lone pairs of phosphorus atoms are in the PdCP
plane to show a suitable conformation to act as a P2-chelate
ligand.6c,7d (3) The conformation of 1 remained unchanged upon
coordination to the carbonyltungsten(0) moieties.6a,b Addition-
ally, the conformation of 1,3-diphosphapropenes 1A and 1B7d,8
In the course of research on low-coordinated phosphorus
compounds stabilized by the Mes* (2,4,6-tri-tert-butylphenyl)
* To whom correspondence should be addressed. Present address:
Department of Chemistry, University of Alabama, Tuscaloosa, AL 35487.
E-mail: myoshifuji@bama.ua.edu.
(1) (a) Regitz, M.; Scherer, O. J. Multiple Bonds and Low Coordination
in Phosphorus Chemistry; Georg Thieme Verlag: Stuttgart, Germany, 1990.
(b) Dillon, K. B.; Mathey, F.; Nixon, J. F. Phosphorus: The Carbon Copy;
Wiley: Chichester, U.K., 1998.
(2) The stable PdP bond: Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu,
K.; Higuchi, T.; J. Am. Chem. Soc. 1981, 103, 4587; 1982, 104, 6167. See
also the following references. PdC compound: Klebach, T. C.; Lourens,
R.; Bickelhaupt, F. J. Am. Chem. Soc. 1978, 100, 4886. PtC bond: Becker,
G.; Gresser, G.; Uhl, W. Z. Naturforsch. 1981, 36B, 16.
(3) Yoshifuji, M. Bull. Chem. Soc. Jpn. 1997, 70, 2881.
(4) (a) Yoshifuji, M. J. Synth. Org. Chem. Jpn. (Yuki Gosei Kagaku
Kyokai-Shi) 2003, 61, 1116. (b) Ozawa, F.; Yoshifuji, M. C. R. Chim. 2004,
7, 747.
(6) (a) Ito, S.; Yoshifuji, M. Chem. Commun. 2001, 1208. (b) Liang,
H.; Nishide, K.; Ito, S.; Yoshifuji, M. Tetrahedron Lett. 2003, 44, 8297.
(c) Liang, H.; Ito, S.; Yoshifuji, M. Z. Anorg. Allg. Chem. 2004, 630, 1177.
(d) Gouygou, M.; Tachon, C.; Koenig, M.; Dubourg, A.; Declercq, J.-P.;
Jaud, J.; Etemad-Moghadam, G. J. Org. Chem. 1990, 55, 5750.
(7) (a) Ito, S.; Liang, H.; Yoshifuji, M. Chem. Commun. 2003, 398. (b)
Liang, H.; Ito, S.; Yoshifuji, M. Org. Lett. 2004, 6, 425. (c) Ito, S.; Liang,
H.; Yoshifuji, M. J. Organomet. Chem. 2005, 690, 2531. (d) Nishide, K.;
Liang, H.; Ito, S.; Yoshifuji, M. J. Organomet. Chem. 2005, 690, 4809.
(5) (a) Mathey, F. Angew. Chem., Int. Ed. 2003, 42, 1578. (b) Weber,
L. Angew. Chem., Int. Ed. 2002, 41. 563.
10.1021/om050972l CCC: $33.50 © 2006 American Chemical Society
Publication on Web 02/07/2006

1,3-Diphosphapropene DeriVatiVes
Organometallics, Vol. 25, No. 6, 2006 1425
Scheme 1
was not affected by chalcogenation, affording the corresponding
3-chalcogeno-1,3-diphosphapropenes 2 and 3: the PdCPdE
(E ) S, O) skeletons are almost coplanar.7
Indeed, 1,3-diphosphapropene derivatives contain rotational
isomerism around the phosphino group, and the conformation
of 1,3-diphosphapropene has been discussed theoretically. The
theoretical calculation pointed out that the conformation ex-
perimentally observed in 1A and 1B is not an energetic
minimum; another conformation was determined as the ener-
getically minimum form.9 In the course of our research on the
PdCP molecular system to develop novel metal complexes of
catalytic activity,6,7 we found that the trimethylsilyl group at
the 2-position of 1,3-diphosphapropene is effective to investigate
the rotational isomerism of the PdCP< molecular system. In
addition, the silyl groups are effective substituents to obtain
several exotic organic compounds.10 In this paper we describe
the preparation, structure, and reactivity of 3,3-diphenyl-1-(2,4,6-
tri-tert-butylphenyl)-2-(trimethylsilyl)-1,3-diphosphapropene (1C),
which shows a conformation different from those of 1,3-
diphosphapropenes 1A and 1B.6c,8 The molecular structures of
2-silyl-1,3-diphosphapropenes are discussed on the basis of
results obtained by X-ray crystallography and theoretical
calculations. Additionally, the 2-(trimethylsilyl)-1,3-diphos-
phapropene 1C was employed as a ligand of the dichloropal-
ladium(II) complex to develop a novel catalyst for a cross-
coupling reaction. The structure of the dichloropalladium(II)
complex bearing 1C was determined by X-ray crystallography,
and the structure effects are discussed.
Figure 1. Thermal ellipsoid plot (50% probability surface) of the
molecular structure of 1C. Hydrogen atoms are omitted for clarity.
Selected bond distances (Å) and angles (deg): P(1)-C(1) ) 1.672-
(3), P(1)-C(2) ) 1.860(3), P(2)-C(1) ) 1.843(3), P(2)-C(20) )
1.843(3), P(2)-C(26) ) 1.845(4), Si-C(1) ) 1.908(3); C(1)-
P(1)-C(2) ) 107.6(1), C(1)-P(2)-C(20) ) 105.7(1), C(1)-P(2)-
C(26) ) 104.2(2), C(20)-P(2)-C(26) ) 102.4(2), P(1)-C(1)-
P(2) ) 116.2(2), P(1)-C(1)-Si ) 134.2(2), P(2)-C(1)-Si )
109.1(2), θ[P(1)-C(1)-P(2)-C(20)] ) -9.7(3), θ[P(1)-C(1)-
P(2)-C(26)] ) 97.8(2).
Chart 2
Results and Discussion
Preparation and Structure of the 2-(Trimethylsilyl)-1,3-
diphosphapropene 1C. (Z)-2-Bromo-1-(2,4,6-tri-tert-butylphen-
yl)-2-(trimethylsilyl)-1-phosphaethene (4) was allowed to react
with butyllithium to generate the (phosphavinyl)lithium inter-
mediate 5 in THF,10c,11 and the solution containing 5 was mixed
with chlorodiphenylphosphine to afford the 2-(trimethylsilyl)-
1,3-diphosphapropene 1C in 71% yield as pale yellow crystals
(Scheme 1). In the 31P NMR spectrum, the sp2 phosphorus and
the sp3 phosphorus were observed at δP 382.7 and -1.6,
respectively. In contrast to the case for 1,3-diphosphapropenes
1A and 1B,6,7 the 2JPP constant of 1C was extremely small (37.1
where the lone pair of the sp2 phosphorus and the phosphino
group are on the same side (Figure 1, Table 1). These findings
indicate that the magnitude of the JPP constant of 1,3-
2
diphosphapropenes is not only dependent on the geometrical
configuration around the PdC plane but also on other factors,
such as the conformation of the 1,3-diphosphapropene skeleton.
The lone pair of the phosphino group of 1C is almost
perpendicular to the PdC bond to show C1 symmetry, whereas
in the case of 1A, the lone pair of the phosphino group is almost
coplanar with the PdC plane to show Cs symmetry (Chart 2).6c
As for the geometrical parameters of 1C, the P(1)-C(1) distance
and the C(1)-P(2)-C(2) angle demonstrate the basic features
of a low-coordinated phosphaalkene.1 The wider P(1)-C(1)-
Si angle might indicate steric repulsion between the Mes* group
and the trimethylsilyl group. The smaller P(1)-C(1)-P(2) and
P(2)-C(1)-Si angles of 1C as compared to the corresponding
data for 1A6c might indicate reduction of the steric congestion
around the diphenylphosphino group, which is suggested by
theoretical calculations (vide infra). The Si-C(1) distance is
slightly longer than the corresponding Si-C distances for
1-(2,4,6-tri-tert-butylphenyl)-2,2-bis(trimethylsilyl)-1-phospha-
ethene (1.891(4), 1.887(4) Å),12 indicating the influence of the
phosphino group.
2
Hz). The small JPP constant is almost equal to that of the
configurational stereoisomer of 1A and 1B, where the lone pair
of the sp2 phosphorus and the phosphino group are on the
opposite side.6 However, the geometrical configuration of 1C
was analyzed by X-ray crystallography to confirm the E form,
(8) (E)-3,3-Bis(p-anisyl)-1-(2,4,6-tri-tert-butylphenyl)-2-methyl-1,3-diphos-
phapropene was analyzed by X-ray crystallography.7d
(9) Dransfeld, A.; Landuyt, L.; Flock, M.; Nguyen, M. T.; Vanquick-
enborne, L. G. J. Phys. Chem. A 2001, 105, 838.
(10) Recent publications: (a) Hwu, J. R.; Chen, B.-L.; Lin, C.-F.; Murr,
B. L. J. Organomet. Chem. 2003, 686, 198. (b) Abe, M.; Kawanami, S.;
Ishihara, C.; Nojima, M. J. Org. Chem. 2004, 69, 5622. (c) Ito, S.; Jin, H.;
Kimura, S.; Yoshifuji, M. J. Org. Chem. 2005, 70, 3537.
(11) (a) Ito, S.; Sekiguchi, S.; Freytag, M.; Yoshifuji, M. Bull. Chem.
Soc. Jpn. 2005, 78, 1142. See also: (b) van der Sluis, M.; Wit, J. B. M.;
Bickelhaupt, F. Organometallics 1996, 15, 174. (c) van der Sluis, M.;
Klootwijk, A.; Wit, J. B. M.; Bickelhaupt, F.; Veldman, N.; Spek, A. L.;
Jolly, P. W. J. Organomet. Chem. 1997, 529, 107. (d) Appel, R.; Casser,
C.; Immenkeppel, M. Tetrahedron Lett. 1985, 26, 3551.
(12) Cowley, A. H.; Jones, R. A.; Lasch, J. G.; Norman, N. C.; Stewart,
C. A.; Stuart, A. L.; Atwood, J. L.; Hunter, W. E.; Zhang, H.-M. J. Am.
Chem. Soc. 1984, 106, 7015.

1426 Organometallics, Vol. 25, No. 6, 2006
Table 1. X-ray Data for Compounds 1C and 6-9
Ito et al.
1C
6
7
8
9‚2CH2Cl2
formula
fw
cryst syst
space group
a/Å
b/Å
c/Å
R/deg
â/deg
γ/deg
V/Å3
C34H48P2Si
546.79
monoclinic
P21/a (No. 14)
10.2492(7)
29.368(1)
11.0728(8)
90
99.791(1)
90
3284.3(3)
4
C39H48O5P2SiW
870.69
monoclinic
P21/c (No. 14)
17.595(1)
10.7937(7)
21.0617(8)
90
95.979(3)
90
3978.1(4)
4
C38H48O4P2SiW
842.68
triclinic
P1h (No. 2)
11.203(5)
19.351(5)
9.385(4)
98.04(2)
102.946(6)
95.85(2)
1944(1)
2
C34H48P2SSi
578.85
orthorhombic
P212121 (No. 19)
17.706(2)
27.180(2)
13.821(2)
90
90
90
6651(1)
8
C34H48P2SiPd‚2CH2Cl2
893.97
monoclinic
P21/n (No. 14)
17.961(4)
14.094(3)
19.103(5)
90
110.279(4)
90
4536(1)
4
Z
T/K
150
1.106
0.189
55
26 757
7249
0.086
223
1.454
3.06
51
23 377
6602
0.063
223
1.439
3.12
55
15 297
8128
0.065
133
1.156
0.250
55
48 169
7629
0.156
223
1.306
0.882
55
22 145
4653
0.076
F
calcd/mg cm-3
µ/mm-1
2θ max/deg
no. of obsd rflns
no. of unique rflns
Rint
R1 (I > 2σ(I))
wR2 (all data)
no of params
GOF
0.046
0.103
334
1.005
0.051
0.106
431
1.079
0.073
0.089
415
1.464
0.060
0.149
686
1.193
0.136
0.355
433
1.831
Table 2. Calculated 31P NMR Data (2JPP (Hz), δP (ppm)) for
I and IIa
2JPP
δP(PdC)
δP(PMe2)
I-C1
I-Cs
II-C1
II-Cs
62.8
411.4
56.1
427.4
505.0
310.2
364.7
38.2
19.7
32.1
4.3
399.0
a B3LYP/6-311+G(2df,p) level.
Theoretical calculations for the model compounds 1,3,3-
trimethyl-2-silyl-1,3-diphosphapropene (I) and 1,2,3,3-tetra-
methyl-1,3-diphosphapropene (II) showed that the C1 form,
which is observed in 1C, is slightly stable than the Cs form by
1.7 kcal/mol (for I) or 1.3 kcal/mol (for II) at the B3LYP/6-
31G(d) level (Figure 2).13 Therefore, the estimated Keq ()[C1]/
[Cs]) constants at 300 K for I and II were 17.4 and 8.9,
respectively. These results are consistent with the calculations
for 1,3-diphosphapropene (HPdCHPH2)9 and are in contrast
to the results for vinylphosphine (CH2dCHPH2).14 Furthermore,
the calculated 31P NMR data at the B3LYP/6-311+G(2df,p)
2
level supported an exceptionally small JPP constant in the C1
conformer, whereas the Cs isomers indicate larger 2JPP constants
(Table 2). Therefore, the C1 conformation of 1C remains even
in solution. Moreover, the C1 conformation of 1C was still
Figure 2. Calculated structures and relative energies for I and II.
between the vicinal hydrogens.15 The calculated 31P NMR
chemical shifts indicated that the sp2 phosphorus atoms in the
C1-symmetric forms afford shifts higher than those in the Cs-
symmetric forms, whereas the sp3 phosphorus atoms in the C1
forms exhibit lower shifts (Table 2). In comparison with the
Cs-symmetric form, the higher shift of the sp2 phosphorus in
the C1-symmetric form is due to π-donation to the PdC group
by the lone-pair electrons on the sp3 phosphorus, which
accordingly shows a lower shift. In the case of the Cs-symmetric
form, the P-Me σ* orbital interacts with the PdC π orbital,
which demonstrates the lower shift of the sp2 phosphorus and
the higher shift of the sp3 phosphorus, respectively.
2
maintained upon heating, while the JPP constant of 43.0 Hz
was observed at 378 K in toluene. The dependence of the
coupling constant between the two nonequivalent phosphorus
atoms on the conformations might be comparable to the Karplus
rule that the coupling constant depends on the dihedral angle
(13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels, A.
D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi,
M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.;
Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick,
D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Cioslowski, J.;
Ortiz, J. V.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi,
I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M.
W.; Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-Gordon,
M.; Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.11.4; Gaussian,
Inc.: Pittsburgh, PA, 1998.
Although 1,3-diphosphapropenes 1A and 1B showed the Cs
conformation in the crystalline state,6c,8 the theoretical investiga-
tion concluded that the C1 form would be the predominant
conformation of the 1,3-diphosphapropene skeleton. In the case
(14) (a) Schade, C.; Schleyer, P. v. R. J. Chem. Soc., Chem. Commun.
1987, 1399. (b) Benidar, A.; Le Doucen, R.; Guillemin, J. C.; Mo´, O.; Ya´n˜ez,
M. J. Mol. Spectrosc. 2001, 205, 252.
(15) (a) Gutowski, H. S.; Karplus, M.; Grant, D. M. J. Chem. Phys. 1959,
31, 1278. (b) Karplus, M. J. Chem. Phys. 1959, 30, 11. (c) Karplus, M. J.
Am. Chem. Soc. 1963, 85, 2870.

1,3-Diphosphapropene DeriVatiVes
Organometallics, Vol. 25, No. 6, 2006 1427
Scheme 2
of vinylphosphine (H2CdCHPH2), the stable conformation has
been determined as the Cs conformation by theoretical and
experimental studies,14 suggesting hyperconjugation between the
CdC π orbital and the P-H σ* orbital. On the other hand, the
PdC bond in 1,3-diphosphapropene has a considerably low
lying LUMO1,4,5 and the lone pair of the phosphino group might
interact with the π orbital of the PdC bond. Furthermore, in
the case of 1C, the silyl group functions as a π-electron
accepting group to enhance the stability of the C1 conformation
of the 1,3-diphosphapropene system, which might cause elonga-
tion of the Si-C(1) distance, as observed in the molecular
structure (vide supra). On the other hand, in the cases of 1,3-
diphosphapropenes 1A and 1B,6c,8 steric hindrance might be
effective in raising the stability of the Cs conformation.
Even if the 31P NMR data correspond to the conformation of
the 1,3-diphosphapropenes, the thermodynamic predominance
of the C1 form over the Cs form is small, suggesting that
interchange between the C1 and Cs forms might occur easily.
Furthermore, the two Ph groups in 1C were equivalently
observed, indicating a rocking motion or a full rotation. We
are currently investigating the molecular dynamics in more
detail.
Figure 3. Thermal ellipsoid plot (50% probability surface) of the
molecular structure of 6. Hydrogen atoms are omitted for clarity.
The p-tert-butyl group is disordered, and the atoms with predomi-
nant occupancy factors (0.54) are displayed. Selected bond distances
(Å) and angles (deg): W-P(2) ) 2.598(2), P(1)-C(1) ) 1.688-
(8), P(1)-C(22) ) 1.856(7), P(2)-C(1) ) 1.854(7), P(2)-C(10)
) 1.850(9), P(2)-C(16) ) 1.835(8), Si-C(1) ) 1.922(8); C(1)-
P(1)-C(22) ) 111.6(4), C(1)-P(2)-C(10) ) 104.0(4), C(1)-
P(2)-C(16) ) 104.3(3), C(10)-P(2)-C(16) ) 102.4(2), P(1)-
C(1)-P(2) ) 107.3(4), P(1)-C(1)-Si ) 131.2(2), P(2)-C(1)-Si
) 121.2(4), θ[P(1)-C(1)-P(2)-C(10)] ) -136.2(4), θ[P(1)-
C(1)-P(2)-C(16)] ) 115.0(4), θ[W-P(2)-C(1)-P(1)] ) -9.3-
(5).
1
constant was reduced. In 13C NMR, the JPC constants of the
PdC moiety are extremely small, probably indicating the effects
of the silyl group. The structure of 7 was unambiguously
determined by X-ray crystallography (Figure 4), revealing the
four-membered chelate ring. Thus, the conformation of the Pd
CP< skeleton of 1C is flexible in coordinating to the carbon-
yltungsten moieties. The structure of 7 is comparable to those
of [1A][W(CO)4]6a and [1B][W(CO)4].6b
Complexation and Sulfurization of the 2-(Trimethylsilyl)-
1,3-diphosphapropene 1C. 1,3-Diphosphapropene 1C was
allowed to react with W(CO)5(thf) at room temperature to afford
the monocoordinated complex 6 (Scheme 2). The coordination
of the phosphino group was determined by observation of JPW
satellite peaks, which appeared only at the higher field signal
in 31P NMR. Similar to the case for the complex of 1A,6a
extremely different magnitudes of 1JPC constants of PdCP in 6
Sulfurization showed other properties of 2-(trimethylsilyl)-
1,3-diphosphapropene 1C (Scheme 2). Compound 1C was
allowed to react with sulfur, and the monosulfurized product 8
was obtained. The structure of 8 was confirmed by X-ray
crystallography, as shown in Figure 5. The structure of 8 shows
a C1 conformation in which the sulfur atom replaces the lone
pair of 1C. Therefore, the sulfur atom might not affect the
conformation of the 1,3-diphosphapropene skeleton, probably
due to the smaller spherical size of sulfur compared with that
1
were observed in the 13C NMR spectrum (one of the JPC
constants is almost 0 Hz). The molecular structure was
unambiguously determined by X-ray crystallography, as dis-
played in Figure 3. In contrast to the conformation of 1C, the
PdCP< skeleton of 6 shows a Cs symmetry, which is similar
to that for the monotungsten(0) complex bearing the ligated 1,3-
diphosphapropene 1A.6a Indeed, the Cs PdCP< conformation
2
2
of 6 might correspond to a JPP constant of 349.6 Hz. Steric
of the W(CO)5 moiety. The JPP constant is close to those of
2A and 2B,7 indicating that rotational isomerism of 3-thioxo-
1,3-diphosphapropene had almost no effect on the 2JPP constant
in 31P NMR.
congestion around the PdCP skeleton, especially due to
repulsion between the trimethylsilyl group and the W(CO)5
moiety, putatively causes this PdCP< conformational isomer-
ization from C1 (1C) to Cs (6). The P-W distance is longer
than the corresponding bond of [1A][W(CO)5] (2.540(1) Å),6a
probably due to the steric bulkiness increasing the P-W
distance.
Preparation and Catalytic Activity of a Palladium(II)
Complex Bearing the Ligated 2-(Trimethylsilyl)-1,3-diphos-
phapropene 1C. One of the purposes of the preparation of 1C
was to develop novel synthetic catalysts bearing 1,3-diphos-
phapropene ligands, and here we demonstrate a novel dichlo-
ropalladium(II) complex with 1C to utilize for a cross-coupling
reaction. Compound 1C was allowed to react with bis-
(acetonitrile)dichloropalladium(II) to afford the corresponding
Irradiation of the monocoordinated tungsten(0) complex 6
caused release of one of the CO ligands and afforded the
corresponding chelate complex 7 as a deep red solid (Scheme
2
2). Upon formation of a four-membered chelate ring, the JPP

1428 Organometallics, Vol. 25, No. 6, 2006
Ito et al.
Figure 4. Thermal ellipsoid plot (50% probability surface) of the molecular structure of 7. Hydrogen atoms are omitted for clarity. Selected
bond distances (Å) and angles (deg): W-P(1) ) 2.459(2), W-P(2) ) 2.533(2), P(1)-C(1) ) 1.681(8), P(1)-C(21) ) 1.842(8), P(2)-
C(1) ) 1.803(7), P(2)-C(9) ) 1.838(8), P(2)-C(15) ) 1.823(8), Si-C(1) ) 1.907(8); P(1)-W-P(2) ) 62.68(6), W-P(1)-C(1) )
103.6(3), W-P(1)-C(21) ) 142.5(2), W-P(2)-C(1) ) 97.3(2), W-P(2)-C(9) ) 124.5(3), W-P(2)-C(15) ) 114.0(3), C(1)-P(1)-
C(21) ) 113.8(3), C(1)-P(2)-C(9) ) 105.9(4), C(1)-P(2)-C(15) ) 110.1(4), C(9)-P(2)-C(15) ) 104.3(4), P(1)-C(1)-P(2) ) 96.3-
(4), P(1)-C(1)-Si ) 134.1(4), P(2)-C(1)-Si ) 128.5(4), θ[P(1)-C(1)-P(2)-C(9)] ) -126.6(4), θ[P(1)-C(1)-P(2)-C(15)] ) 121.3(4).
Table 3. The Sonogashira Reaction Catalyzed by
Dichloropalladium(II) Complex 9
entry
R
yield/%
1
H
96
2
Br
85
3
Me
OMe
I
60
4
57a
65c,d
5b
a Diphenylbutadiyne was obtained in 5% yield. b Two molar equivalents
of phenylacetylene was used. c Product:
d p-IC6H4CtCPh was also obtained in 15% yield.
coupling reaction of aryl iodides with phenylacetylene afforded
the corresponding acetylene derivatives (Table 3). Iodobenzene
gave the cross-coupling product almost quantitatively (entry 1),
and the cross-coupling with p-bromoiodobenzene indicated the
predominant reactivity toward iodide over bromide, affording
4-bromodiphenylacetylene (entry 2). On the other hand, electron-
donating substituents at the para position of aryl iodides showed
relatively low reactivity (entries 3 and 4). In the reaction with
p-iodoanisole, diphenybutadiyne was obtained as a side product
(see the footnote for Table 3). p-Diiodobenzene and 2 molar
equiv of phenylacetylene gave 1,4-bis(phenylethynyl)benzene
in moderate yield together with a mono cross-coupling product,
4-iododiphenylacetylene (entry 5). As shown in Table 3, the
air-stable 9 displayed considerable catalytic activity in the
Sonogashira cross-coupling reaction, although some limitations
were also recognized.
The molecular structure of 9 was unambiguously determined
by X-ray crystallography, as shown in Figure 6. Although the
quality of the data for 9‚2CH2Cl2 is insufficient to discuss the
metric parameters in detail, the four-membered-ring structure
with the PdCP skeleton is obvious. The P(1)-Pd distance is
shorter than the P(2)-Pd bond, which is comparable to the case
for 7. The acute P-Pd-P angle of 9, which is close to the
corresponding value for [Ph2PCH2PPh2][PdCl2] (72.68(3)°),16
Figure 5. Thermal ellipsoid plot (50% probability surface) of the
molecular structure of 8. One of the two independent molecules is
displayed. Hydrogen atoms are omitted for clarity. Selected bond
distances (Å) and angles (deg): S(1)-P(2) ) 1.959(3), P(1)-C(1)
) 1.689(8), P(1)-C(2) ) 1.853(7), P(2)-C(1) ) 1.842(7), P(2)-
C(20) ) 1.828(8), P(2)-C(26) ) 1.832(7), Si(1)-C(1) ) 1.906-
(7); C(1)-P(1)-C(2) ) 108.5(3), S(1)-P(2)-C(1) ) 113.8(2),
S(1)-P(2)-C(20) ) 110.1(3), S(1)-P(2)-C(26) ) 112.8(3),
C(1)-P(2)-C(20) ) 107.4(3), C(1)-P(2)-C(26) ) 105.6(3),
C(20)-P(2)-C(26) ) 106.7(3), P(1)-C(1)-P(2) ) 111.1(4),
P(1)-C(1)-Si(1) ) 133.8(4), θ[P(1)-C(1)-P(2)-S(1)] ) -136.6-
(3), θ[P(1)-C(1)-P(2)-C(20)] ) -14.4(5), θ[P(1)-C(1)-P(2)-
C(26)] ) 99.1(4).
dichloropalladium(II) complex 9 in 95% yield (Scheme 2).
When the spectroscopic data are taken into account, the structure
of 9 corresponds to a dichloropalladium(II) complex bearing
the ligated 1B.6b In the presence of 9, the Sonogashira cross-

1,3-Diphosphapropene DeriVatiVes
Organometallics, Vol. 25, No. 6, 2006 1429
Figure 6. Thermal ellipsoid plot (30% probability surface) of the molecular structure of 9‚2CH2Cl2. Hydrogen atoms and the solvent
molecules (CH2Cl2) are omitted for clarity. Selected bond distances (Å) and angles (deg): Pd-Cl(1) ) 2.358(4), Pd-Cl(2) ) 2.339(4),
Pd-P(1) ) 2.207(4), Pd-P(2) ) 2.255(4), P(1)-C(1) ) 1.68(1), P(1)-C(2) ) 1.82(1), P(2)-C(1) ) 1.83(1), Si-C(1) ) 1.89(2); Cl-
(1)-Pd-Cl(2) ) 95.7(2), Cl(1)-Pd-P(1) ) 100.4(1), Cl(1)-Pd-P(2) ) 168.9(1), Cl(2)-Pd-P(1) ) 163.9(1), Cl(2)-Pd-P(2) ) 94.7-
(1), P(1)-Pd-P(2) ) 69.3(1), C(1)-P(1)-C(2) ) 117.4(6), P(1)-C(1)-P(2) ) 92.3(7), P(1)-C(1)-Si ) 134.8(8), P(2)-C(1)-Si )
132.2(8), θ[Pd-P(1)-C(1)-P(2)] ) -0.7(7).
University. Compound 4 was prepared by the procedures described
in the literature.10c,11
might determine the catalytic activity together with the presence
of the PdC double bond.4,5
Preparation of 1C. To a solution of 4 (1.00 g, 2.27 mmol) in
THF (20 mL) was added butyllithium (2.3 mmol, 1.6 M solution
in hexane, 1 M ) 1 mol dm-3) at -78 °C. After 10 min, to the
reaction mixture containing 5 was added chlorodiphenylphosphine
(2.3 mmol), and this mixture was warmed to room temperature.
After 2 h, the volatiles were removed and the residual materials
were purified by silica gel column chromatography (hexane/AcOEt
) 19:1) to afford 1C as pale yellow crystals (0.88 g, 71%). Mp:
124-125 °C. 31P{1H} NMR (162 MHz, CDCl3): δ 382.7 (d, 2JPP
Conclusion
We have demonstrated that the 2-(trimethylsilyl)-1,3-diphos-
phapropene 1C, prepared from the corresponding (phospha-
ethenyl)lithium 5, shows a conformation around the phosphino
group with C1 symmetry, in contrast to the Cs symmetry
displayed by 1,3-diphosphapropenes 1A and 1B. Theoretical
calculations suggested that the C1 conformation of the PdCP<
system is predominant, and the Cs conformation of 1,3-
diphosphapropenes 1A and 1B might be affected by the steric
effects of the substituents. These results suggest that the
conformation of 1,3-diphosphapropene depends on the substitu-
ent at the 2-position. The C1 conformation of 1C was trans-
formed into the Cs conformation upon coordination of the
carbonyltungsten(0) moiety, as shown in the structures of 6 and
7, whereas heating as well as sulfurization, affording 8, had
almost no influence on the conformation of 1C. The structure
of the palladium(II) complex 9 was analyzed by X-ray crystal-
lography, and some catalytic activity of 9 for the Sonogashira
reaction was confirmed. Investigations concerning the molecular
dynamics of the 1,3-diphosphapropenes and the catalytic activity
of metal complexes to understand the novel effects of the silyl
group are in progress.
2
) 37.1 Hz), -1.6 (d, JPP ) 37.1 Hz). 1H NMR (400 MHz,
CDCl3): δ 7.87-7.85 (m, 4H, arom), 7.58-7.51 (m, 8H, arom),
1.70 (s, 18H, o-t-Bu), 1.51 (s, 9H, p-t-Bu), 0.53 (s, 9H, SiMe3).
13C{1H} NMR (101 MHz, CDCl3): δ 184.0 (dd, 1JPdC ) 88.1 Hz,
1JP-C ) 62.0 Hz, PdC), 153.7 (s, o-C of Mes*), 151.0 (s, p-C of
Mes*), 142.8 (dd, 1JPC ) 79.4 Hz, 3JPC ) 6.4 Hz, ipso-C of Mes*),
133.8 (pt, (1JPC+3JPC)/2 ) 15.0 Hz, ipso-Ph), 135.1 (d, 2JPC ) 20.4
3
Hz, o-Ph), 129.1 (s, p-Ph), 128.6 (d, JPC ) 7.1 Hz, m-Ph), 122.4
(s, m-C of Mes*), 38.8 (s, o-CMe3), 35.5 (s, p-CMe3), 34.1 (d,
3
4JPC ) 7.3 Hz, o-CMe3), 32.0 (s, p-CMe3), 0.4 (d, JPC ) 8.2 Hz,
SiMe3). Anal. Calcd for C34H48P2Si: C, 74.69; H, 8.85. Found: C,
73.94; H, 8.86. ESI-MS: calcd for M+ (C34H48P2Si + H) 547.3073,
found 547.3074.
Preparation of 6. To a solution of 1C (350 mg, 0.641 mmol)
in THF (10 mL) was added W(CO)5(thf) (ca. 1.00 mmol, prepared
from W(CO)6 by irradiation for 12 h with a medium-pressure 100
W Hg lamp at 0 °C in THF), and the mixture was stirred at room
temperature for 12 h. The volatiles were removed, and the residual
materials were purified by silica gel column chromatography (10/1
hexane/chloroform) and recrystallization from hexane to afford 6
as yellow crystals (167 mg, 30%). Mp: 240-242 °C dec. 31P{1H}
Experimental Section
General Methods. All manipulations were carried out under an
argon atmosphere by means of the standard Schlenk techniques or
in a glovebox. All solvents employed were dried by appropriate
methods. H, 13C{1H}, and 31P{1H} NMR spectra were recorded
on a Bruker Avance 400 spectrometer in CDCl3 with Me4Si (1H,
13C) and H3PO4 (31P), respectively, as internal or external standard.
IR spectra were measured on a Horiba FT-300 spectrometer as KBr
pellets. Mass spectra were recorded on a Bruker APEX3 spectrom-
eter. Elemental analyses were performed in the Instrumental
Analysis Center for Chemistry, Graduate School of Science, Tohoku
2
1
NMR (162 MHz, CDCl3): δ 437.3 (d, JPP ) 349.6 Hz), -29.3
2
1
1
(d, JPP ) 349.6 Hz, satellite JPW ) 245.4 Hz). H NMR (400
MHz, CDCl3): δ 7.78-7.76 (m, 4H, arom), 7.48-7.46 (m, 6H,
arom), 7.39 (s, 2H, arom), 1.61 (s, 18H, o-t-Bu), 1.35 (s, 9H, p-t-
Bu), -0.81 (s, 9H, SiMe3). 13C{1H} NMR (101 MHz, CDCl3): δ
201.6 (d, 2JPC ) 21.3 Hz, COax), 198.9 (dd, 2JPC ) 9.8 Hz, 4JPC
)
1
6.4 Hz COeq), 175.0 (d, JPdC ) 76.5 Hz, PdC), 154.5 (s, o-C of
Mes*), 151.8 (s, p-C of Mes*), 139.7 (dd, 1JPC ) 79.6 Hz, 3JPC
44.7 Hz, ipso-C of Mes*), 138.3 (dd, 1JPC ) 35.6 Hz, 3JPC ) 13.7
)
(16) Steffen, W. L.; Palenik, G. J. Inorg. Chem. 1976, 15, 2432.

1430 Organometallics, Vol. 25, No. 6, 2006
Ito et al.
Hz, ipso-Ph), 132.5 (d, 2JPC ) 11.3 Hz, o-Ph), 130.0 (d, 4JPC ) 1.3
7.99 (m, 4H, arom), 7.76-7.72 (m, 2H, arom), 7.65-7.60 (m, 6H,
3
3
Hz, p-Ph), 128.6 (d, JPC ) 9.2 Hz, m-Ph), 122.5 (d, JPC ) 1.2
Hz, m-C of Mes*), 38.9 (s, o-CMe3), 35.3 (s, p-CMe3), 34.8 (d,
4JPC ) 7.2 Hz, o-CMe3), 31.6 (s, p-CMe3), 2.5 (s, SiMe3). IR
(KBr): ν(CO) 2065, 1981, 1932, 1907 cm-1. Anal. Calcd for
C39H48O5P2SiW: C, 53.80; H, 5.56. Found: C, 53.98; H, 5.58.
Preparation of 7. A solution of 6 (110 mg, 0.126 mmol) in
THF (5 mL) was irradiated with a medium-pressure 100 W Hg
lamp at 0 °C for 12 h. The volatiles were removed, and the residual
materials were purified by silica gel column chromatography (10/1
hexane/AcOEt) to afford 7 as red crystals (62 mg, 58%). Mp: 240-
arom), 1.85 (s, 18H, o-t-Bu), 1.39 (s, 9H, p-t-Bu), -0.45 (s, 9H,
1
SiMe3). 13C{1H} NMR (101 MHz, CDCl3): δ 185.1 (d, JPdC
)
6.6 Hz, PdC), 157.1 (s, o-C of Mes*), 157.0 (s, p-C of Mes*),
4
134.3 (d, JPC ) 11.7 Hz, o- or m-Ph), 129.1 (d, JPC ) 2.9 Hz,
1
p-Ph), 129.7 (d, JPC ) 12.5 Hz, o- or m-Ph), 126.8 (dd, JPC
)
55.8 Hz, 3JPC ) 4.7 Hz, ipso-Ph), 125.0 (d, 3JPC ) 7.9 Hz, m-C of
Mes*), 122.9 (dd, 1JPC ) 33.7 Hz, 3JPC ) 10.3 Hz, ipso-C of Mes*),
39.6 (s, o-CMe3), 35.8 (s, p-CMe3), 35.4 (s, o-CMe3), 31.1 (s,
p-CMe3), -0.4 (s, SiMe3). Anal. Calcd for C34H48Cl2P2PdSi: C,
56.40; H, 6.68. Found: C, 56.10; H, 6.93.
242 °C dec. 31P{1H} NMR (162 MHz, CDCl3): δ 320.0 (d, 2JPP
)
The Sonogashira Reaction with 9: Typical Procedure. A
solution of iodobenzene (2.0 mmol), phenylacetylene (2.0 mmol),
9 (0.050 mmol), and copper(I) iodide (0.050 mmol) in triethylamine
(8 mL) was stirred for 4 h at room temperature. The volatiles were
removed, and the residue was extracted with hexane. Silica gel
column chromatography (hexane) of the hexane extracts afforded
diphenylacetylene (96% yield).
X-ray Crystallography. A Rigaku RAXIS-IV imaging-plate
detector with graphite-monochromated Mo KR radiation (λ )
0.710 70 Å) was used. The structure was solved by direct methods
(SIR92)17 and expanded using Fourier techniques (DIRDIF94).18
A symmetry-related absorption correction using the program
ABSCOR19 was applied for 7 and 9‚2CH2Cl2. Attempts to solve
the structure of 6 from the diffraction data, including the absorption
correction, failed. The non-hydrogen atoms were refined anisotro-
pically. Hydrogen atoms (calculated) were refined isotropically. The
data were corrected for Lorentz-polarization effects. Structure
solution, refinement, and graphical representation were carried out
using the teXsan package.20 The X-ray crystallographic data for
1C (CCDC-288846), 6 (CCDC-288848), 7 (CCDC-2888499), 8
(CCDC-288850), and 9 (CCDC-288847) can be obtained via
www.ccdc.cam.ac.uk/data request/cif.
1
2
57.2 Hz, satellite JPW ) 211.0 Hz), -8.4 (d, JPP ) 57.2 Hz,
satellite 1JPW ) 186.3 Hz). 1H NMR (400 MHz, CDCl3): δ 7.67-
7.62 (m, 4H, arom), 7.47-7.45 (m, 6H, arom), 7.43 (d, 4JPH ) 1.2
Hz, 2H, arom), 1.78 (s, 18H, o-t-Bu), 1.34 (s, 9H, p-t-Bu), -0.60
(s, 9H, SiMe3). 13C{1H} NMR (101 MHz, CDCl3): δ 212.7 (dd,
2JPC ) 32.5 Hz, 2JPC ) 8.2 Hz, COeq), 210.8 (dd, 2JPC ) 21.8 Hz,
2
2
2JPC ) 9.3 Hz, COeq), 206.4 (dd, JPC ) 9.8 Hz, JPC ) 6.4 Hz
1
COax), 191.0 (d, JPdC ) 3.2 Hz, PdC), 155.8 (s, o-C of Mes*),
1
3
153.6 (s, p-C of Mes*), 134.8 (dd, JPC ) 34.1 Hz, JPC ) 18.5
Hz, ipso-Ph), 132.5 (d, 2JPC ) 13.1 Hz, o-Ph), 130.6 (d, 4JPC ) 1.7
3
3
Hz, p-Ph), 128.9 (d, JPC ) 10.1 Hz, m-Ph), 122.8 (d, JPC ) 4.3
Hz, m-C of Mes*), 39.4 (s, o-CMe3), 35.6 (s, p-CMe3), 35.1 (s,
o-CMe3), 31.5 (s, p-CMe3), 0.9 (s, SiMe3) (ipso-C of Mes* could
not be determined). IR (KBr): ν(CO) 2015, 1915, 1905, 1888 cm-1
.
Anal. Calcd for C38H48O4P2SiW: C, 54.16; H, 5.74. Found: C,
54.04; H, 5.71.
Preparation of 8. A solution of 1C (0.50 g, 0.99 mol) and sulfur
(0.99 mmol as S) in toluene (10 mL) was refluxed for 2 h. After
the mixture was cooled to room temperature, the volatiles were
removed and the residual materials were purified by silica gel
column chromatography (19/1 hexane/AcOEt) to afford 8 as pale
yellow crystals (0.52 g, 91%). Mp: 97-98 °C. 31P{1H} NMR (162
MHz, CDCl3): δ 409.6 (d, 2JPP ) 140.5 Hz), 50.7 (d, 2JPP ) 140.5
Acknowledgment. This work was supported in part by
Grants-in-Aid for Scientific Research (Nos. 13303039 and
14044012) from the Ministry of Education, Culture, Sports,
Science and Technology, of Japan. We thank Prof. Takeaki
Iwamoto, Tohoku University, for the ab initio MO calculations.
1
Hz). H NMR (400 MHz, CDCl3): δ 8.06-8.01 (m, 4H, arom),
7.50-7.48 (m, 6H, arom), 7.40 (s, 2H, arom), 1.52 (s, 18H, o-t-
Bu), 1.36 (s, 9H, p-t-Bu), 0.23 (s, 9H, SiMe3). 13C{1H} NMR (101
1
1
MHz, CDCl3): δ 176.7 (dd, JPdC ) 85.3 Hz, JP-C ) 26.0 Hz,
PdC), 153.9 (s, o-C of Mes*), 151.8 (s, p-C of Mes*), 138.7 (dd,
1JPC ) 77.5 Hz, 3JPC ) 29.8 Hz, ipso-C of Mes*), 135.3 (dd, 1JPC
) 81.9 Hz, 3JPC ) 6.5 Hz, ipso-Ph), 133.2 (d, 3JPC ) 9.8 Hz, m-Ph),
Supporting Information Available: X-ray crystallographic data
(as CIF files) for 1C and 6-9. This material is available free of
charge via the Internet at http://pubs.acs.org.
4
3
131.4 (d, JPC ) 2.7 Hz, p-Ph), 128.4 (d, JPC ) 12.2 Hz, o-Ph),
122.6 (s, m-C of Mes*), 38.9 (s, o-CMe3), 35.4 (s, p-CMe3), 34.5
4
OM050972L
(d, JPC ) 7.0 Hz, o-CMe3), 31.8 (s, p-CMe3), 3.0 (s, SiMe3). IR
(KBr): ν(PdS) 706, 652 cm-1. Anal. Calcd for C34H48P2SSi: C,
70.55; H, 8.36; S, 5.54. Found: C, 70.40; H, 8.10; S, 5.20.
Preparation of 9. A solution of 1C (290 mg, 0.53 mmol) and
Cl2Pd(MeCN)2 (0.53 mmol) in dichloromethane (30 mL) was stirred
for 12 h. The reaction mixture was diluted with 10 mL of hexane
to give yellow precipitates of 9. The precipitates were filtered and
washed with hexane (365 mg, 95%). Mp: 216-219 °C dec. 31P-
(17) Altomare, A.; C. Burla, M.; Camalli, M.; Cascarano, M.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, 27, 435.
(18) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits, J. M. M. The DIRDIF94 Program System;
Technical Report of the Crystallography Laboratory, University of Nijmegen,
Nijmegen, The Netherlands, 1994.
(19) Higashi, T. Program for Absorption Correction; Rigaku Corp.,
Tokyo, 1995.
(20) Crystal Structure Analysis Package; Molecular Structure Corp., The
Woodlands, TX, 1985 and 1999.
2
{1H} NMR (162 MHz, CDCl3): δ 260.6 (d, JPP ) 110.0 Hz),
-27.3 (d, 2JPP ) 110.0 Hz). 1H NMR (400 MHz, CDCl3): δ 8.05-